RESEARCH showing that a large daily dose of vitamin D can dramatically cut the risk of developing common cancers was given a cautious welcome today.

Researchers in California found that the `natural' form of the vitamin, known as D3, could dramatically reduce the chances of developing breast, ovarian and colon cancer, as well as others, by up to 50%.

But a leading cancer charity was cautious about the claims, with a spokeswoman saying the evidence linking vitamin D levels with cancer risk was complex and confusing.

"There is evidence to suggest that the vitamin plays a role in keeping cells healthy," said Sara Hiom, head of health information at Cancer Research UK.

"But further research is needed to understand what role vitamin D may play in preventing cancer."

The research concluded that taking 1,000 international units (IU) of the vitamin daily could lower an individual's cancer risk by 50%.

Such large doses of vitamin D must be treated with caution.

More than 2,000 IU a day can lead to the body absorbing too much calcium and possibly damaging the liver and kidneys.

D3 is normally produced in the skin by the action of sunlight, but is also obtained from certain foods.

Dietary sources are limited, however. A glass of milk, for instance, contains only 100 IU of the vitamin.

The research, published in the American Journal of Public Health, reviewed 63 studies looking at the relationship between blood levels of vitamin D and cancer risk.

The study found that people in the north-eastern US and darker-skinned individuals were at increased risk due to a lack of sunshine- generated vitamin D.